Multi-function electronic timing circuit



Jan. 1, 1957 s. c. ROCKAFELLOW 2,776,383

MULTI FUNCTION ELECTRONIC TIMING CIRCUIT Filed April 21, 1952 2 Sheets-Sheet 2 IN V EN TOR.

.Sru/MT C. Roar/1:544 w BY M arr RNEY United States Patent This invention relates to electronic timing circuits and more particularly to timing circuits for controlling a series of functions such as used in conjunction with resistance welding machines.

Most gun type resistance welders use four timing functions in their operation, namely, squeeze time, the time for the electrodes to be brought together, weld time, the time for which actual current flows through the electrodes, hold time, the time required for the Welded portion to cool sufficiently before opening the electrodes and off time, the time necessary to move the electrodes to a new position while the electrodes are open.

In the usual operation, a relay closes at the start of the sequence to actuate a valve which allows either air or hydraulic means to close the electrodes together. After sufiicient time has elapsed to bring the points together and build up sufiicient pressure, another relay is caused to close and the weld current starts to flow through the electrodes. This relay is held closed for a predetermined time and is then caused to open, thus terminating the fiow of welding current.

In present timers, circuit effecting this opening of the last-named relay is a vulnerable circuit because the conduction of an electronic tube is necessary to open said relay. If this tube should fail in its operation, then the weld current would continue to flow indefinitely, thereby burning the work and harming the electrodes. Where the eelctrodes include die structures, this can be very expensive.

In an attempt to meet this condition there has in the past been provided a variety of circuits eliminating the necessity for a tube to commence conducting in order to turn off the welding current. Some of these, such as my copending application Serial No. 239,593, accomplish this objective satisfactorily but they do it only by incorporating an extra relay. This addition of a relay subjects the circuit to the double objection of a somewhat increased cost, due to the cost of the relay, but, worse, it subjects the circuit to the possibility of early breakdown resulting from the fact that relays often fall before tubes normally fail and thus the presence of three relays in a circuit materially increases the likelihood of failure over a circuit having only two relays.

Thus, the presently known circuits above indicated, although performing their ultimate objective satisfactorily, introduce such additional problems as to limit seriously their usefulness.

Accordingly, a principal object of the invention is to provide a circuit which when the welding current is once started, does not require the conduction of an electronic tube to turn off said current.

A further object of the invention is to provide such a circuit in which, when the welding current has been started, the conduction of an electronic tube is not required to turn off the current and wherein such objective is accomplished without the addition of a further relay.

A further object of the invention is to provide a circuit,

as aforesaid, in which said objectives may be accomplished without requiring a materially more complicated circuit than those previously known.

. A further object of the invention is to provide a circuit, as aforesaid, which is simple and which may be embodied in operative apparatus without expense materially, if any, greater than according to conventional practice. I

A further object of the invention is to provide a circuit, as aforesaid, 'from which a timer can be built which is sturdy, accurate and relatively free of maintenance requirements.

Other objects and purposes of the invention will be apparent to persons acquainted with apparatus of this general sort upon reading the following specification and inspection of the accompanying drawings.

In the drawings:

Figure 1 represents a circuit diagram illustrating a preferred form of the invention.

Figure 2 is a fragmentary circuit diagram illustrating a modification.

In meeting the objects and purposes above set forth, I have utilized a circuit broadly similar to that shown in my Patent No. 2,573,360 and in my co-pending application Serial No. 239,593. Nevertheless, it will be understood that, inasmuch as the subject matter of this invention is primarily directed toward the closing, holding closed for a predetermined period of time, and subsequent opening of a single relay, many of its features will be applicable to other circuits than the ones specifically here shown and that the use of the particular timing circuit here used for illustrative purposes should be considered as illustrative only and not as limiting, excepting only as expressly stated otherwise.

Turning now to Figure 1 whereinis illustrated one preferred embodiment of the invention, there is provided a pair of bus conductors 1 and 2, which bus conductors are adapted to be energized to a conventional manner from any convenient source of alternating potential and are continuously so energized throughout the entire op eration of the timing circuit. A plurality of electric discharge devices, hereinafter designated in detail, are connected to each other and to said bus conductors for the purpose of controlling the relays 3 and 4. The relay 3 controls the opening and closing of the welding electrodes and the relay 4 controls the turning on and ofi of the welding current. a

Each of said electric discharge devices are of the gas filled type having an anode and a cathode and one or two control electrodes commonly known as thyratrons and hence, for purposes of convenience in reference, and not as limiting, the electric discharge devices will be designated as thyratrons hereinafter.

The thyratron 6 is connected at its anode through the winding 7 of the relay 3 to the bus conductor 2, and at its cathode by the conductor 11 through the switch 8,

, which may be any conventional form of manually operated switch, to the bus conductor 1. The contacts 9 of said relay 3 may be connected in a conventional manner to etfect'the opening and closingof the welding electrodes. I

The thyratron 12 is connected at its anode by the conductor 13 through the primary winding 14 of the first transformer 15 to the bus conductor 2. Said thyratron 12 is connected at its cathode by the conductor 16 through the contacts 17 of the relay 3 to a point on conductor 11 between the switch 8 and the cathode of the thyratron 6. The contacts 18 of the relay 3 are connected around the switch 8. Manually operated switch 21 is connected around said contacts 17. A conductor 22 connects the cathode of the thyratron 12 through a 0 resistance 23, of relatively high value, as 50,000 ohms, to the bus conductor 2. The control electrode 24 of the thyratron 12 is connected by the conductor 26 through the variable resistance 27 to the bus conductor 1. A capacitor 28 is connected around the variable resistance 27.

In order to reduce transient effects, it is desirable, though not essential, also to connect a rectifier 31 around the primary winding 14. A resistor 32 is also included in series with said rectifier for the protection thereof, if desired. The thyratron 34 is connected by its anode through the primary winding 36 of a second transformer 37 and thence through the secondary winding 38 of thefirst transformer and the conductor 39 to the bus conductor 1. The cathode of said thyratron 34 is connected 15 by the conductor 41 directly to the bus conductor 1.

A conductor 42 connects a junction point 43, located between the anode of the thyratron 12 and the primary winding 14, through the rectifier 44 and thence through the conductor 46 and the variable resistance 47 to the bus conductor 1. The capacitor 48 is connected around the variable resistance 47. A conductor 51 connects the bus conductor 2 through the rectifier 52 through a resistance 53 and thence through a resistance 54 to the bus conductor 1. A capacitor 56 is connected around the resistance 54. A resistor 57 is connected from the conductor 46 to a junction point 58, a resistor 59 is connected from the conductor 51 to the junction point 58 and said junction point is connected by the conductor 61 to the control electrode 62 of the thyratron 34. The sense of the rectifier 44 is such that its positive side is connected to the capacitor 48 and the sense of the rectifier 52 is such that its negative side is connected to the capacitor 56. The values of the several parts are such that the positive potential imposed at the junction point 58 by the capacitor 48 is normally materially larger than the negative potential imposed at said junction point by the capacitor 56. The exact amount by which said positive potential exceeds said negative potential is controlled by the variable resistance 47.

The thyratron 64 is connected by its anode through the winding .66 of the relay 4 to the bus conductor 2. The contacts 67 of said relay 4 are adapted to control the flow of welding current in a conventional manner. The cathode of said thyratron 64 is connected by a conductor 68 to the bus conductor 1. The conductor 69 connects the negative side of the. capacitor 56 through the secondary winding 71 of the second transformer 37 and thence through the protecting resistance 72 to the control electrode 73 of the thyratron 6.4.

The thyratron 74 is .connected by its anode through the variable resistance 76 to the bus conductor 2 and the capacitance 77 is connected around the variable resistance 76. The cathode of the said thyratron '74 is connected by the conductor 78 to the bus conductor 1. A conductor 79 connects a point on the conductor s61. between the junction point 58 and the control electrode 62 to the control electrode 810i the thyratron 74.

The thyratron 84 is connected from its cathode by the conductor 86 to the bus conductor 2. It is further 0 connected by its anode through a variable resistance .87 and a conductor 88 through a switch, here the switch 8, to the bus conductor 1. A capacitor 89 is connected around the variable resistance 87. The anode of the thyra on 84 is also onne e y e onduc or 91. to the control electrode 92 of the thyratron 6. The conduct: tor 93 connects the anode of the thyratron 74 to the control electrode 94 of the thyratron 84.

Operation In its at rest condition, prior to the closing of the initiating switch 8, the apparatus is in the following condition:

D e to s open at o c u t e yrat n 6.. s n0 conductive and the relay 3 is de-e'nergized. Accordingly,

the electrodes of the welding machine, which are con trolled by the contact 9 of the relay 3, are open.

The capacitor 28 is charged by current flowing between the two bus conductors through the variable resistance 27, the grid and cathode of the thyratron 12 and the resistance 23. The capacitor 48 is likewise charged by current flowing between the bus conductors through the primary winding 14, the rectifier 44 and the variable resistance 47. Similarly the capacitor 56 is charged by current flowing between the bus conductors through the resistance 54, the resistance 53 and the rectifier 52.

The thyratron 12 is non-conductive due to its open cathode circuit and the thyratron 34 is non-conductive inasmuch as its anode potential depends upon the energization of the secondary winding 38 of the transformer 15 by conduction of the thyratron 12. The thyratron 64 is non-conducting due to a negative potential appearing on its control electrode 73 by reason of the charging of the capacitor 56. The thyratron 74 is conducting inasmuch as the positive potential on the side of the capacitor 48, which is connected to the junction point 58 and thence to the control electrode 81, is materially larger than the negative potential on the side of the capacitor 56 which is also connected to the junction point 58. The thyratron 84 is held blocked by the anode potential of the thyratron 74 being applied to the control electrode 94 through the conductor 93.

Upon the closing of the initiating switch 8, thyratron 6 conducts, energizing the relay 3 and thereby closing its contacts 9, 17 and 18. The closing of the contacts 9 energizes the solenoid which closes the welding electrodes. The closing of the contacts 18 shunts the initiating switch 8 to hold said thyratron 6 conductive when the initiating switch is released.

The closing of the relay contacts 17 brings the cathode of the thyratron 12 to the potential of the bus conductor 1 to which the grid 24 is also connected through the variable resistance 27, and thus the grid to cathode conduction through said thyratron 12 is terminated. This terminates the charging of the capacitor 28 and applies a negative potential from said capacitor onto the grid 24 for holding said thyratron 12 blocked until the charge on said capacitor 28 drains off through the variable resistance 27. The time required for the capacitor 28 to drain ofi through the resistance 27 to a sufficiently low point to permit the conduction of the thyratron 12 is the time delay between the closing of the contacts 9, and thereby the closing of the welding electrodes and the initiating of the welding current. This time period is commonly known as squeeze time and is controlled by the setting of the variable resistance 27 With the conduction of the thyratron 12, the junction point 43 is effectively brought to the potential of the bus conductor 1, and hence flow of current through the variable resistance 47 is terminated. This stops the charging of v the capacitor 48 and it commences to drain out through the variable resistance 47 with the results to be hereinafter described. Simultaneously, the conduction of the thyratron 12 energizes the secondary winding 38 of the transformer 15 and thereby provides an anode potential for the thyratron 34. This effects conduction of said thyratron 34 and thus energizes the secondary winding 71 of the transformer 37. Such energization of said secondary winding overcomes the ne' ative bias placed onto the control electrode 73 by the capacitor 56 and thus permits conduction of the thyratron 64. This energizes the winding 66 of the relay 4 and closes the contacts 67 of said relay whereby the flow of Welding current commences.

In the meantime, the capacitors 48 and 56 have both been draining through their respectively connected resistances 47 and 54. However, the resistance 47 is materially less than the resistance 54 so that the negative charge on the. capacitor 56 ultimately predominates over the positive charge on the capacitor 48 and in a predeterminable period, selected according to the setting of the variable resistance 47, the predominance of said negative charge is sufiicient to effect blocking of the thyratron 34. With the blocking of said thyratron, there ceases to be pulses generated in the secondary winding 71 for overcoming the negative charge from said capacitor 56 applied to the control electrode 73, and said negative charge is again applied to said control electrode 73 and the thyratron 64 ceases to conduct. This de-energizes the relay 4 and opens its contacts 67 and thus terminates the flow of the welding current.

Simultaneously with the blocking of the thyratron 34 the negative blocking potential on conductor 61 is also applied by the conductor 79 to the control electrode 81 of the thyratron 74 by which said thyratron 74 is blocked. This terminates the charging of the capacitor 77 and same begins to drain through the variable resistance 76. This represents the hold time. As soon as said capacitor drains sufliciently that its charge as applied through the conductor 93 to the control electrode 94 becomes insufiicient to hold the thyratron 84 blocked, said thyratron 84 will conduct and apply a potential through the conductor 91 to the control electrode 92 of the thyratron 6. This blocks thyratron 6 and the relay 3 is de-energized. With the de-energization of the relay 3, the relay contacts 9 open and the welding electrodes are thereby permitted to open.

The conduction of the thyratron 84 also charges the capacitor 89, its capacity being such that a single pulse is sufficient to render it fully charged.

The de-energizing of the relay 3, also opens the relay contacts 17 and 18 and thereby restores a system to the at rest condition described above. This at rest condition includes the re-energizing of the control electrode 94 from the anode of the thyratron 74 and thereby effecting the blocking of the thyratron 84. This terminates the charging of the capacitor 89 and the biasing of the control electrode 92 from the anode of the thyratron 84 but the potential on the capacitor 89 will hold the control electrode 92 under negative potential until said charge drains off through the variable resistance 87. Thus, the thyratron 6 will be held blocked for a period of time, the off time, determined by the time required for the charge on the capacitor 89 to diminish to a level sufiiciently low that the thyratron 6 is no longer blocked.

When the charge on the control electrode 92 is sufficiently low as to permit the thyratron 6 again to become conductive, whether or not it will do so depends upon the position of the manually operated switches 8 and 21. For repeat operation, the initiating switch 8 is held closed and the switch 21 is held open. Thus, during the period when the thyratron 6 is blocked, that is, during the off period, the contacts 17 of the relay 3 are open which terminates the conduction of the thyratron 12 by opening its cathode circuit. Thus, grid to cathode conduction again starts through the thyratron 12 and, in a manner detailed above, the capacitor 28 again becomes charged. Similarly, the capacitor 48 again becomes charged so that its positive potential imposed at the junction point 58 again overcomes the negative potential of the capacitor 56 and thus renders the thyratron 34 ready for conduction upon the appearance of an anode supply. Similarly, conduction again starts through the thyratron 74 and, as above set forth, the charging of the capacitor 77 effects blocking of the thyratron 84.

As soon as the charge on the capacitor 89 drains out through the variable resistance 87 and the thyratron 6 is thereby again rendered conductive, with the switch 8 being held closed the cycle above described again is initiated in the manner above set forth.

When it is desired to operate the device for single operations, the switch 21 is held closed. Thus, the thyratron 12 cannot be de-energized until the initiation switch 8 is open. Thus, thyratron 74 will be held non-conductive by the continuing negative charge on the capacitor 56 and this permits thyratron 84 to continue conduction and thereby hold thyratron 6 blocked for as long as initiation switch 8 is held closed. When said switch is open, the thyratron 6 ceases to conduct and the whole systemreturns to the at rest condition outlined above.

It will be appreciated that throughout the above described operation, it is at no point necessary to await the firing of any particular thyratron in order to shut off the flow of welding current. The welding current is permitted to flow only by the overcoming of the potential blocking thyratron 64 and originating in the capacitor 56 which overcoming is effected by the conduction of the thyratron 34. For so long as said thyratron conducts, the welding current is permitted to continue. However, upon the failure of any thyratron in the system, the welding current will either be turned off immediately or, at the most, it will finish out a given welding period but will not initiate another one.

Particularly, failure of a thyratnon 6 will de-energize the relay 3 and at the end of the cycle of operations in which such failure occurs it will restore the entire system to its at rest condition. Failure of thyratron 12 will prevent the energization of the transformer 15 and thereby prevent the supplying of an anode potential to the thyratron 34 whereby to prevent its operation in overcoming the blocking potential normally held on the control electrode 73. Failure of the thyratron 34 will likewise terminate, or prevent, the overcoming of the blocking potential normally held on the control electrode 73 and, whenever it occurs, it will instantly render the thyratron 64 permanently blocked and thereby immediately terminate the flow of welding current. Failure of the thyra tron 64 will de-energize the relay 4 and terminate the welding current. Failure of the thyratron 74 will terminate charging of the capacitor 77 which will then commence discharging through the variable resistance 76 and as soon as said capacitor discharges to a predetermined value it will permit conduction through the thyratron 84 and result in the blocking of the thyratron 6 and opening of the welding electrodes. Inasmuch as under such conditions the thyratron 84 will remain conductive, the thyratron 6 will remain blocked and a new cycle will not be permitted to start. Failure of the thyratron 84 will prevent initiating of the oif time period and, in effect, result in an indefinite continuation of the hold time. However, it will have no effect upon the termination of flow of welding current and, inasmuch as a new cycle will not start no damage will occur pending discovery and remedying of the difliculty.

Modification of Figure 2 The embodiment of the invention illustrated in Figure 2 proceeds upon the same basic organization as that illustrated and described in connection with Figure 1, excepting only that the charges of the capacitors 48 and 56 are combined in the respective thyratrons 34 and 74 by being connected to independent grids therein rather than by being combined at the junction point 58 (Figure 1). In the form shown in Figure 2, the parts numbered with the same numerals as appearing in Figure 1 are all corresponding parts' and are connected together in same manner as above described in connection with Figure 1. However, in place of the resistors 57 and 59 the conductor 61 and the conductor 79, there are provided the following parts: (a) the conductor 101 connects the conductor 46 at a point between the capacitor 48 and the rectitier 44 through a protective resistor 102 with each of the control grids 62 and 81, respectively, of the thyratrons 34 and 74, and (b) the conductor 103 connects a point on the conductor 51 between the capacitor 56 and the resistance 53 with, respectively, the screen grids 94 and of the thyratrons 34 and 74.

The operation of this modification is the same as described above with the combined effect of the capacitors 48 and 56 being applied to the thyratrons 34 and 74 to hold same conductive and non-conductive, for the same purposes and with the same results as set forth above, by the joint operations of the grids in each thyratron.

Accordingly, I have provided apparatus accomplishing the objects and purposes above set'forth.

While I have utilized certain preferred embodiments of the invention for illustrating same, it will be understood that various modifications will be'possible which will be apparent to persons acquainted with apparatus of this general sort and such modifications will all be within the scope of the hereinafter appended claims excepting as said claims by their own terms expressly require otherwise.

I claim:

1'. In a sequence timing device, the combination comprising: a load; first and second bus conductors, said bus conductors being connectible to a source of alternating current; a first thyratron having its anode connected through the load to the second bus conductor and its cathode connected to the first bus conductor; a source of constant potential and means connecting the negative side of said last-named source to the control electrode of said first thyratron and means connecting the positive side of said last named source to the cathode of said first thyratron; a first transformer, the secondary winding of which is connected in series between the negative side of said source of constant potential and the control electrode of said first thyratron; a second transformer; a second thyratron; means connecting the cathode of said second thyratron to said first bus conductor and means connecting its anode through the primary winding of said first transformer, thence through the secondary winding of said second transformer to said first bus conductor; means providing a time constant circuit including a capacitor and a resistor in parallel with each other; a rectifier; means connecting one end of said time constant circuit to said first bus conductor and means connecting the other end of said time constant circuit to the positive terminal of said rectifier and means connecting the negative terminal of said rectifier to one end of a primary Winding of said second transformer, the other end of said primary winding being connected to said second bus conductor; mean including current conducting and interrupting means connecting said one end of said lastnamed primary winding to said first bus conductor; the values of the several said parts being such that the normal positive charge on said capacitor is materially greater than the value of said source of constant negative potential; means connecting the positive side of said rectifier to the control electrode of said second thyratron.

2. The device defined in claim 1 in combination with means controlling a further timing function and including a third thyratron; means applying the negative potential from said constant source and the positive potential from said capacitor jointly onto said third thyratron for controlling the conduction thereof.

3, A sequence timing circuit comprising, in combination: first and second bus conductors connectible to a source of alternating current; a first thyratron; a first load; a first switch; means serially including said load connecting the anode of said first thyratron to said second bus conductor; means including said switch connecting the cathode of said first thyratron to said first bus conductor; a second thyratron; a transformer; and means connecting the anode of said second thyratron through the primary winding of said transformer to said second bus conductor and means connecting the cathode of said second thyratron through a relatively high resistance to said second bus conductor; a second switch and means connecting the cathode of said second thyratron through said switch to said first bus conductor; a time constant circuit including a capacitor and a resistor in parallel with each other and means connecting one end thereof to said first bus conductor and the other end thereof to the control electrode of said second thyratron; a second time constant circuit including a capacitance and a resistance in parallel with each "other and means connecting one end thereof to said first bus conductor; a first rectifier, and means connecting the other end of said time constant circuit to the positive side of said rectifier and other means connecting the negative side of said rectifier to the anode of said second thyratron; a voltage divider circuit including a pair of resistances, and a second rectifier and means connecting same in series with each other and between said bus conductors and said rectifier being connected in such polarity that its positive terminal is connected to the second bus conductor; a second capacitance bridging one of said resistances and having a positive and a negative terminal; a third thyratron; a second transformer; means connecting the cathode of said third thyratron to said first bus conductor and means connecting the anode of said third thyratron through the primary winding of said second transformer to the secondary winding of said first transformer and thence to said first bus conductor; a fourth thyratron and a second load; means connecting the cathode of said fourth thyratron to said first bus conductor and means connecting the anode of said fourth thyratron through said second load to said second bus conductor; means connecting the negative terminal of said second capacitance through the secondary winding of said second transformer to the control electrode of said fourth thyratron; a fifth thyratron and a third time constant circuit having a capacitance and a resistance in parallel with each other; means connecting the cathode of said fifth thyratron to said first bus conductor and other means connecting the anode of said fifth thyratron through said time constant circuit to said second bus conductor; means connecting the negative side of said second capacitance and the positive side of said first capacitance to a common point and means connecting said common point to the control means within said third and fifth thyratrons for blocking same or permitting same to conduct depending on the charge of said first capacitance with respect to the charge of said second capacitance; a sixth thyratron and a fourth time constant circuit including a capacitance and a resistance in parallel with each other; means connecting the cathode of said sixth thyratron to said second bus conductor and means connecting the anode of said sixth thyratron to the control electrode of said first thyratron and means also connecting the anode of said sixth thyratron through said last-named time constant circuit and through a switch to said first bus conductor; and means connecting the anode of said fifth thyratron to the control electrode of said sixth thyratron.

4. The combination defined in claim 3 wherein the anode of the sixth thyratron is connected through said fourth time-constant circuit to the cathode of said first thyratron, whereby said first switch become said last named switch.

5. A sequence timing circuit comprising, in combination: a pair of bus conductors connectible to a source of alternating current; a first thyratron; a first load; a first switch; means serially including said first load connecting the anode of said first thyratron to said second bus conductor; means including said first switch connecting the cathode of said first thyratron to said first bus conductor; a second thyratron; a first transformer; and means connecting the anode of said second thyratron through the primary winding of said first transformer to said second bus conductor and means connecting the cathode of said second thyratron through a relatively high resistance to said second bus conductor; a second switch and means connecting the cathode of said second thyratron through said second switch to said first bus conductor; a time constant circuit including a resistance and a capacitance in parallel with each other and means connecting one end thereof to said first bus conductor and the other end thereof to the control electrode of said second thyratron; a second time constant circuit including a capacitance and a resistance in parallel with each other and means connecting one end thereof to said first bus conductor; a rec.- t e nd mean connect n he t e e o said t me constant circuit to the positive side of said rectifier and other means connecting the negative side of said rectifier to the anode of said second thyratron; biasing means providing a source of constant potential; a third thyratron; a second transformer; means connecting the cathode of said third thyratron to said first bus conductor and means connecting the anode of said third thyratron through the primary Winding of said second transformer to the secondary winding of said first transformer and thence to said first bus conductor; a fourth thyratron and a second load; means connecting the cathode of said fourth thyratron to said first bus conductor and means connecting the anode of said fourth thyratron through said second load to said second bus conductor; means connecting said biasing source through the secondary winding of said second transformer to the control electrode of said fourth thyratron; a fifth thyratron and a third time constant circuit including a capacitance and a resistance in parallel with each other; means connecting the cathode of said fifth thyratron to said first bus conductor and other means connecting the anode of said fifth thyratron through said third time constant circuit to said second bus conductor; means connecting the negative side of said biasing source and the positive side of said first capacitance to a common point and further means connecting said point to the control means within said third and fifth thyratrons for blocking same or permitting same to conduct depending on the charge of said first capacitance with respect to the value of the negative potential at said biasing source; a sixth thyratron and a fourth time constant circuit comprising a capacitance and a resistance in parallel with each other; means connecting the cathode of said sixth thyratron to said second bus conductor and means connecting the anode of said sixth thyratron to the control electrode of said first thyratron and means also connecting the anode of said sixth thyratron through said last-named time constant circuit and through a switch to said first nus conductor; and means connecting the anode of said fifth thyratron to the control electrode of said sixth thyratron.

6. In a sequence timing device, the combination comprising: a load; first and second bus conductors, said bus conductors being connectible to a source of alternating current; a first thyratron having its anode connected through the load to the second bus conductor and its cathode connected to the first bus conductor; a source of constant potential and means connecting the negative side of said last named source to the control electrode of said first thyratron and means connecting the positive side of said last named source to the cathode of said first thyratron; a first transformer, the secondary winding of which is connected in series between the negative side of said source of constant potential and the control electrode of said first thyratron; a second transformer; a second thyratron; means connecting the cathode of said second thyratron to said first bus conductor and means connecting its anode through the primary winding of said first transformer, thence through the secondary winding of said second transformer to said first bus conductor; means providing a time constant circuit including a capacitor and a resistor in parallel with each other; a rectifier connected in series with said time constant circuit to form a series group; means connecting one end of said series group to said first bus conductor and means connecting the other end of said series group to one end of a primary winding of said second transformer, the other end of said primary winding being connected to said second bus conductor; means including current conducting and interrupting means connecting said one end of said last named primary Winding to said first bus conductor; the values of the several said parts being such that the normal positive charge on said capacitor is materially greater than the value of said source of constant negative potential; means responsive to the value of said negative potential from said constant source and to the positive potential of said capacitor for controlling the conduction of said second thyratron which will act through said first transformer to control the conduction of said first thyratron.

7. In a sequence timing device, the combination comprising: a load; first and second bus conductors, said bus conductors being connectible to a source of alternating current; a first thyratron having its anode connected through the load to the second bus conductor and its cathode connected to the first bus conductor; a source of constant potential and means connecting the negative side of said last named source to a junction point and means connecting the positive side of said last named source to the cathode of said first thyratron; a first transformer, the secondary winding of which is connected in series between the negative side of said source of constant potential and the control electrode of said first thyratron; a second transformer; a second thyratron; means connecting the cathode of said second thyratron to said first bus conductor and means connecting its anode through the primary winding of said first transformer, thence through the secondary winding of said second transformer to said first bus conductor; means providing a time constant circuit including a capacitor and a resistor in parallel with each other; a rectifier; means connecting one end of said time constant circuit to said first bus conductor and means connecting the other end of said time constant circuit to the positive terminal of said rectifier and means connecting the negative terminal of said rectifier to one end of a primary Winding of said second transformer, the other end of said primary Winding being connected to said second bus conductor; means including current conducting and interrupting means connecting said one end of said last named primary winding to said first bus conductor; the values of the several said parts being such that the normal positive charge on said capacitor is materially greater than the value of said source of constant negative poten tial; means connecting the positive side of said rectifier to said junction point; a conductor connecting said junction point to the control electrode of said second thyratron.

8. In a sequence timing device, the combination comprising: a load; a source of alternating current; a first thyratron having its anode connected through said load to one side of said source and its cathode connected to the other side of said source; a source of constant potential and means connecting the negative terminal of said last named source to the control electrode of said first thyratron; and means connecting the positive terminal of said last named source to the cathode of said first thyratron; a capacitor and a resistance connected around said capacitor; a connection from one side of said capacitor to one side of said alternating source and means including a rectifier connecting the other side of said capacitor to the other side of said alternating source; a circuit including a second thyratron for supplying positive potential to the control electrode of said first thyratron; means connecting the positive side of said capacitor and the negative side of said source of constant potential to said control electrode of said second thyratron; means connecting the positive side of said source of constant potential and the negative side of said capacitor to the cathode of said second thyratron; means including a switch shunting said rectifier and said capacitor.

9. In a sequence timing device, the combination comprising: a load; a source of alternating current; a first thyratron having its anode connected through said load to one side of said source and its cathode connected to the other side of said source; a source of constant potential and means connecting the negative terminal of said last named source to the control electrode of said first thyratron; means connecting the positive terminal of said last 'named source to the cathode of said first thyratron; a capacitor and means charging said capacitor; a circuit including a second thyratron for supplying positive po- :tential to the control electrode of said first thyratron; means connecting the positive side of said capacitor and the negative side of said source of constant potential to said control electrode of said second thyratron; means connecting the positive side of said source of constant potential and the negative side of said capacitor to the cathode of said second thyratron; means including a switch shunting said capacitor and said means charging said capacitor.

10. In a sequence timing device, the combination comprising: a load; a source of alternating current; a first thyratron having its anode connected through said load to one side of said source and its cathode connected to the other side of said source; a source of constant potential and means connecting the negative terminal of said last named source to the control electrode of said first thyratron; and means connecting the positive terminal of said last named source to the cathode of said first thyratron; a capacitor and means charging said capacitor; a circuit including a potential responsive switch for supplying positive potential to the control electrode of said first thyratron; means connecting said switch to the side of said capacitor producing a potential rendering said switch conductive and to the side of said source of constant potential rendering said switch non-conductive; means in cluding another switch shunting said capacitor and said means charging said capacitor.

11. In a sequence timing device, the combination comprising: a load; a source of alternating current; an electric discharge device having its anode connected through said load to one side of said source and its cathode connected to the other side of said source; a first capacitor and a first resistance in parallel therewith and means connecting one terminal of said first capacitor to one side of said source and the other terminal of said first capacitor to the other side of said source, said last named means including a first rectifier and a resistance in series with each other; means connecting the negative side of said first capacitor to the control electrode of said electric discharge device and means connecting the positive terminal of said capacitor to the cathode of said electric discharge device; a second capacitor and a second resistance connected around said second capacitor; means connecting one side of said second capacitor to one side of said source and means including a second rectifier connecting the other side of said second capacitor to the other side of said source; low resistance means including a switch shunting said second rectifier; a circuit for supplying positive potential to the control electrode of said electric discharge device and a second electric discharge device controlling the energization of said last named circuit; means connecting the positive side of said second capacitor and the negative side of said first capacitor to the control electrode of said second electric discharge device; said second resistance being materially less than said first rc sistance; whereby when said switch is open both of said capacitors will charge but said second capacitor will charge to a higher level than the charge on said first capacitor and therefore render said second electric discharge device conductive, and when said switch is closed, the charge on each of said capacitors will drain through their respectively connected resistances and the charge on said second capacitor will drain more rapidly than the charge on the first capacitor, thereby rendering said second electric discharge device non-conductive at a predeterminable time.

12. In a sequence timing device the combination comprising: a load; a source of alternating current; an electric discharge device having its anode connected through said lead to one side of said source and its cathode connected to the other side of said source; a first capacitor and a first resistance in parallel therewith and means connecting one terminal of said first capacitor to one side of said source and the other terminal of said first capacitor to the other side of said source, said last named means including a first rectifier and a resistance in series with each other; means connecting the negative side of said first capacitor to the control electrode of said electric discharge device and means connecting the positive terminal of said capacitor to the cathode of said electric discharge device; a second capacitor and a second resistance connected around said second capacitor; means connecting one side of said second capacitor to one side of said source and means including a second rectifier connecting the other side of said second capacitor to the other side of said source; a switch shunting said second rectifier; a circuit for supplying positive potential to the control electrode of said electric discharge device and a second electric discharge device controlling the energization of said last named circuit; means connecting the positive side of said second capacitor and the negative side of said first capacitor to the control electrode of said second electric discharge device; said second resistance being materially less than said first resistance; whereby when said switch is open both of said capacitors will charge but said second capacitor will charge to a higher level than the charge on said first capacitor and therefore render said second electric discharge device conductive, and when said switch is closed, the charge on each of said capacitors will drain through their respectively connected resistances and the charge on said second capacitor will drain more rapidly than the charge on the first capacitor, thereby rendering said second electric discharge device non-conductive at a predeterminable time.

13. In a sequence timing device, the combination comprising: a load; a source of alternating current; a first thyratron having its anode connected through said load to one side of said source and its cathode connected to the other side of said source; a first capacitor and a first resistance in parallel therewith and means connecting one terminal of said first capacitor to one side of said source and the other terminal of said first capacitor to the other side of said source, said last named means including a first rectifier and a resistance in series with each other; means connecting the negative side of said first capacitor to the control electrode of said first thyratron and means connecting the positive terminal of said capacitor to the cathode of said thyratron; a second capacitor and a second resistance connected around said second capacitor; means connecting one side of said second capacitor to one side of said source and means including a second rectifier connecting the other side of said second capacitor to the other side of said source; means including a switch for simultaneously terminating the supply of potential to both of said capacitors; a circuit for supplying positive potential to the control electrode of said thyratron and a second thyratron controlling the energization of said last named circuit; means connecting the positive side of said second capacitor and the negative side of said first capacitor to the control electrode of said second thyratron; said second resistance being materially less than said first resistance; whereby when said switch is open both of said capacitors will charge but said second capacitor will charge to a higher level than the charge on said first capacitor and therefore render said second thyratron conductive, and when said supply of potential to the capacitors is terminated the charge on each of said capacitors will drain through their respectively connected resistances and the charge on said second capacitor will drain more rapidly than the charge on the first capacitor, thereby rendering said second thyratron non-conductive at a predeterminable time.

14. The device defined in claim 1 wherein said source of constant potential is a rectifier and a capacitor connected in series between said bus conductors, said connection including sufficient resistance that the maximum charge on said last named capacitor is always less than the maximum charge on said first named capacitor.

15. In a sequence timing device, the combination comprising: a load; a source of alternating current; a thyratron connected in series with said load between the terminals of said source; a first chargeable source of constant potential and means connecting the negative terminal of said first source to the control electrode of said thyratron and means connecting the positive terminal of said first source to the cathode of said thyratron; a circuit supplying positive potential to the control electrode of said thyratron, said circuit including a switch rendered non-conductive by a negative potential; a connection from the negative side of said first source to said switch and connected for rendering it non-conductive; a. second chargeable source of constant potential and means connecting the positive terminal thereof to one terminal of said switch and means connecting the negative terminal thereof to another terminal of said switch, the polarity of such connection being such that a positive potential from said second source Will render said switch conductive; means simultaneously charging both of said sources, said second source being charged to a potential of value higher than that of said first source; means simultaneously diminishing the value of potentials on said sources with the value of the potential on said second source being diminished at a rate faster than the rate of diminution of the potential on said first source; whereby said thyratron is conducting when both of said sources are at their maximum values of potential and said thyratron becomes non-conducting at a determinable point during the diminution of the values of the potential provided by said respective sources.

16. In a sequence timing device, the combination comprising: a load; a source of alternating current; a thyratron connected in series with said load between the terminals of said source; a first source of constant potential including a first capacitor and means connecting the negative terminal of said first source to the control electrode of said thyratron and means connecting the positive terminal of said first source to the cathode of said thyratron; a circuit supplying positive potential to the control electrode of said thyratron, said circuit including a switch rendered non-conductive by a negative potential; a connection from the negative side of said first source to said switch and connected for rendering it non-conductive; a second source of constant potential including a second capacitor and means connecting the positive terminal thereof to one terminal of said switch and means connecting the negative terminal thereof to another terminal of said switch, the polarity of such connection being such that a positive potential from said second source wilt render said switch conductive; means simultaneously charging the capacitors comprising both of said sources, said second source being charged to a potential of value higher than that of said first source; means simultaneously diminishing the value of potentials on said sources with the value of the potential on said second source being diminished at a rate faster than the rate of diminution of the potential on said first source; whereby said thyratron is conducting when both of said sources are at their maximum values of potential and said thyratron becomes non- 14 conducting at a determinable point during the diminution of the values of the potential provided by said respective sources.

17. In a sequence timing device, the combination comprising: a load; a source of alternating current; a thyratron connected in series with said load between the terminals of said source; a first source of constant potential including a first capacitor and means connecting the negative terminal of said first source to the control electrode of said thyratron and means connecting the positive terminal of said first source to the cathode of said thyratron; a circuit supplying positive potential to the control electrode of said thyratron, said circuit including a switch rendered non-conductive by a negative potential; a connection from the negative side of said first source to said switch and connected for rendering it nonconductive; a second source of constant potential including a second capacitor and means connecting the positive terminal thereof to one terminal of said switch and means connecting the negative terminal thereof to another terminal of said switch, the polarity of such connection being such that a positive potential from said second source will render said switch conductive; a common source simultaneously charging both of said sources, and the circuit of said first source including more resistance serially connected with said first capacitor than the resistance serially connected with said second capacitor whereby said second source is charged to a potential of value higher than that of said first source; means simultaneously diminishing the value of potentials on said sources with the value of the potential on said second source being diminished at a rate faster than the rate of diminution of the potential on said first source; whereby said thyratron is conducting when both of said sources are at their maximum values of potential and said thyratron becomes non-conducting at a determinable point during the diminution of the values of the potential provided by said respective sources.

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